Brief State of Art and background

Although flexible electrically heated mats in general are not entirely new to art conservation, their use was marginal and virtually undeveloped. For example in paintings conservation electrically heated mats (heat blankets) were employed in early heating tables, and Helmut Ruhemann suggested an application similar to ours in 1959 using the Electrothermal Rubber Sheet®. In the same year, Alain Boissonnas described the USKON conductive rubber mat and its use in an early heating table and perhaps similar applications were used by other conservators, but not documented or developed any further. More recently, a silicone heated mat, mounted on a solid support and controlled manually with a dimmer and external thermometer was used by Jos van Och (Stichting Restauratie Atelier Limburg SRAL) in Maastricht for the lining of the colossal Mesdag Panorama mural in The Hague (1990-1996).

First steps towards the pre-IMAT prototypes were taken in 2003, when the first mobile high precision flexible mild heating system was designed and applied successfully by N. Olsson and T. Markevicius in the treatment of large scale mural paintings on canvas by H.S. Sewell (1899-1975) in Oregon City, Oregon, USA.

The first prototype was made of silicon rubber and wound wire heating elements, connected to a custom designed control unit with an external thermal sensor. Later, a second prototype was created in 2005, with some improvements in its design and was used by Markevicius in his studio in Amsterdam and in the National Gallery of Canada. Both prototypes and later designed heaters have been used since then in the treatment of numerous artworks, which differ in size, period and materials and the results have solicited considerable interest from the conservation community.

While several important features, such as versatility, mobility and temperature control meeting the conservation standards, was achieved fairly well in silicone rubber/wound wire (pre-Imat) heaters, the entire “wish list” was unobtainable with traditional materials. The pre-Imat heaters could not be designed as transparent or translucent mats, the breathability and permeability to water vapours was impossible and the voltage of 110 V or 240 V (for larger size mats) and the PD of 0.23 W/cm2 – 0.3 W/cm2 was required for the mild heating up to 85˚ C (which is above the range of most structural treatments).

In order to achieve the target objectives in the IMAT “wish list” it was necessary to change radically the heating technology and to invent an entirely different heating technology by replacing the resistance wiring with thermally and electrically conductive nanomaterials, such as carbon nanotubes or silver nanowires, which will allow design of highly accurate heaters, which could be very thin, lightweight, transparent and breathable and where the low voltage application is possible. The low power and voltage requirement would be key from a safety and "green" power consumption point of view, but also would allow greater diffusion of a state of the art conservation tool, making it easily adapted to any environment, basically wherever there is regular current.